The chief problem in the Chicago water supply is to protect the waters of Lake Michigan by changing the flow to the Mississippi and at the same time not to divert enough water to seriously disturb the level of the Lakes and the flow of the St. Lawrence. Whether this can be accomplished by using the maximum quantity of 10,000 cubic feet per second, only the future can determine. At the same time international relations must not be strained and the friendship and collaboration of our neighbors on the North are necessary to accomplish the best results. In the end it will doubtless be found that the citizens of all the towns and cities bordering the Great Lakes and their connecting rivers will have to purify their sewage before it is returned to the lacustrine circulation.